Known examples of antibiotics having a clerodane-type diterpene structure include terpentecin (MF730-N6) produced by a microorganism belonging to the genus Kitasatosporia [refer to EP 205981A; The Journal of Antibiotics, 38, 1664 (1985); and ibid. 38, 1819 (1985)] and clerocidin (PR-1350) produced by a microorganism belonging to the genus Oidiodendron [refer to U.S. Pat. No. 4,576,961; The Journal of Antibiotics, 36, 753 (1983); and Tetrahedron Letters, 25, 465 (1984)].
Both of clerodane-type diterpene antibiotics usually occur as an equilibrium mixture of tautomers which are chemically equivalent with each other. For example, it is known that clerocidin is present in the form of an equilibrium mixture of monomers such as hydroxyaldehyde (compound A) and hemiacetal (compound B) or a dimer (compound C), as shown by the following formulae. ##STR1##